Hybrid drive system

ABSTRACT

A hybrid drive system includes an internal combustion engine with an output shaft. An energy converter is connected to the output shaft via a coupling. The energy converter has first and second rotors which are rotatable at different speeds in relation to each other. At least one of the rotors is provided with one or more windings which are supplied with current from a current converter. The current converter is supplied with direct current from a direct current source. A transmission with variable gear ratio is coupled to one of the rotors. The transmission and the current converter cooperate via a control arrangement. The control arrangement comprises a control unit for controlling rotational speed and torque of the internal combustion engine and the energy converter.

BACKGROUND OF THE INVENTION

The present invention relates to a hybrid drive system and also relatesto a control device for a hybrid drive system.

It is previously known to arrange a hybrid drive system as a vehicledrive. For example DE-A-41 18 678 relates to a hybrid drive system whichcomprises an internal combustion engine, an electric battery and a driveshaft which can be driven by the internal combustion engine and thebattery. The transmission of the energy from the internal combustionengine and the energy of the battery to the drive shaft is effected viaa slip ring motor or an energy converter comprising two concentricrotors. The outer rotor, which is joined to the shaft of the internalcombustion engine, is provided with permanent magnets and the innerrotor, which is joined to the drive shaft, is provided with windingswhich are supplied with alternating current with the aid of slip rings,and which are coupled via a current-converter to the battery. The driveshaft is joined to a transmission of a fixed gear ratio whichdistributes the rotory movement of the drive shaft to the wheel axles ofthe vehicle.

U.S. Pat. No. 3,796,278 relates to a control system for a hybrid drivesystem which, in one embodiment, comprises an internal combustionengine, a current source, an electromagnetic clutch, an electric motorand a gearbox. The internal combustion engine is coupled to the electricmotor via the electromagnetic clutch. The output shaft of the electricmotor is joined to the gearbox. The electromagnetic clutch isconstructed of two concentric rotors, one of which is provided with awinding supplied with current from the current source. The hybrid drivesystem is controlled by control units which regulate the current supplyto the electric motor.

SUMMARY OF THE INVENTION

One purpose of the present invention is to achieve a hybrid drive systemwhich makes possible optimal distribution of load between the internalcombustion engine and the battery with regard to environmentalrequirements, such as the emissions of the system and with regard tooperating life and operating characteristics.

An additional purpose is to achieve a hybrid drive system which makesdriving possible by means of an electrically driven energy converterwhich is supplied by a power source and an internal combustion engine,the mean value over time of the expended energy from the power sourcebeing zero or nearly zero over a defined time period.

A further purpose of the invention is to achieve a control device whichmakes possible in an advantageous manner optimum operation of the hybriddrive system.

A hybrid drive system with the characteristic features of the presentinvention achieves exceptional efficiency in the internal combustionengine since the variable transmission in combination with theelectrical energy converter permits increased freedom to allow theinternal combustion engine to work at optimum rpm and torque.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with reference to anumber of examples which are shown in the accompanying drawings.

FIG. 1 shows a series hybrid system according to known technology.

FIG. 2 shows a parallel hybrid system according to known technology.

FIGS. 3A-3C show in diagram form how the outputs of the components in ahybrid drive system interact.

FIG. 4 is a schematic drawing of a hybrid drive system according to theinvention.

FIGS. 5A-5D show the characteristics of an internal combustion engine inthe form of efficiency and emission diagrams.

FIG. 6 shows a block diagram of a control device in a hybrid drivesystem according to the invention.

FIG. 7 shows a partially sectioned side view of an energy converteraccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Hybrid drive systems for vehicles can essentially be divided into twogroups: series hybrid systems and parallel hybrid systems. Series hybridsystems, as shown in FIG. 1, consist essentially of an internalcombustion engine 1, an AC generator 2, a rectifier 3, acurrent-converter 4, an AC motor 5, which in most cases is a cageinduction motor, a gearbox 6 and a battery 7. The rpm and torque of theinternal combustion engine 1 can in principle, in this system, bedetermined with complete freedom.

Parallel hybrid systems are based, as can be seen in FIG. 2, on aninternal combustion engine 11, an electric motor 12, a current-converter13, a battery 14 and a gearbox 15. The speed of the internal combustionengine 11 and the electric motor 12 is the same in this system. Via thecurrent-converter 13, the power of the battery 14 can be supplied to adrive shaft 16 and thus give added torque to the system.

FIG. 3A shows a graph of an internal combustion engine producingconstant power at a constant rpm. Since the power consumption of avehicle varies, the energy converter will work as an electric motor whenpower is to be supplied to the drive wheels of the vehicle. When thereis an excess of kinetic energy in the vehicle or when the vehicle is tobe braked, power is sent to the battery which is thus charged, and inthis case the converter acts as a generator. This is shown in FIG. 3B,with the areas above the time axis representing motor mode and the areasbelow the time axis representing generator mode for the converter. Forhybrid operation, the internal combustion engine is set so that itprovides a power corresponding to the mean power requirement for thetype of operation in question. Any increase or decrease in powerrequirement is compensated with the aid of the converter, as shown inFIG. 3C.

FIG. 4 shows a schematic drawing of a hybrid drive system according tothe invention where the hybrid drive system is a drive means for awheeled vehicle. In the hybrid drive system, energy from the internalcombustion engine 21 is combined with energy from a source of directcurrent, such as a battery 22, in an energy converter 23, which isprovided with two concentric rotors 24, 25, having individual shafts.The first rotor 24, which can be the inner rotor, is coupledmechanically to the output shaft 26 of the internal combustion engine21, and the output shaft 26 can be locked or braked by a mechanical orelectrical clutch 27, which couples the internal combustion engine 21 toone of the rotors 24, 25 of the energy converter 23. The second rotor25, which can be the outer rotor, can be coupled to a wheel axle 28 viaa gearbox 29 with continuously variable gear ratio of the type CVT(Continuously Variable Transmission). Continuously variabletransmissions are known to the person skilled in the art, and thereforetheir construction and function will not be described in more detailhere.

With a CVT connected to the hybrid drive system, the internal combustionengine 21 can be set to work at an rpm and torque which is optimum forefficiency and emissions. This optimum rpm and torque is determined bythe characteristics of the internal combustion engine 21, which areobtained by engine testing at different loads on the internal combustionengine 21. Examples of the characteristics of an internal combustionengine are shown in FIGS. 5A-5D in the form of efficiency and emissiondiagrams. The curves in the diagram shown in FIG. 5A represent variousvalues of the efficiency of an internal combustion engine at variousrpms and torques. FIGS. 5B-5D show the curves for CO-, NOx- andHC-emissions, respectively. By combining the hybrid drive system with aCVT, the most advantageous operating condition or operating point of theinternal combustion engine 21 for the type of operation in question, canbe obtained on the basis of known characteristics of the internalcombustion engine 21. Different types of operation can occur, e.g.highway driving or city driving. By coupling a control device accordingto the present invention to the hybrid drive system and the CVT, theoperating properties of a vehicle with the hybrid drive system as adrive source can be optimized for output, efficiency and emissions.

The internal combustion engine 21 thus provides the desired torque forthe type of operation in question, and the rpm is controlled in theenergy converter 23 to compensate for a change in the rpm of the shaftbetween the energy converter 23 and the CVT. If the load of the vehiclewheels changes, the fear ratio in the CVT is changed, and the rpm iscompensated in the converter 23 so that the set rpm and torque for theinternal combustion engine 21 remain constant.

The energy converter 23 is provided with current via a current-converter30 which converts the direct current from the battery 22 intoalternating current. The current-converter 30 is, in accordance with theexample, coupled to the outer rotor 25 of the energy converter 23 bymeans of slip rings 31.

Electrically, the energy converter 23 can be constructed as apermanently magnetized synchronous machine or a separately magnetizedsynchronous machine with or without brushes. The two rotors 24, 25 ofthe energy converter 23 can rotate freely, independently of each other.The rotational direction of the outer rotor 25 follows the rotationaldirection of the inner rotor 24 during hybrid operation, which meansthat a combination of the internal combustion engine 21 and the energyconverter 23 drives the vehicle. For electrical operation, the rotor 24coupled to the internal combustion engine 21 is locked by means of theclutch 27 and the second rotor 25 can rotate in either rotationaldirection. The torque of the rotors 24, 25 is equal in magnitude butwith opposite signs. The outer rotor 25 is provided with windings whichare supplied with current via the slip rings 31, and the inner rotor 24is provided with permanent magnets.

The power distribution between the internal combustion engine 21 and thebattery 22 is controlled by the relative difference in rpm between theouter rotor 25 and the inner rotor 24. The relative difference in rpmcan be positive or negative. The sign of the relative difference in rpmis decisive for which mode of operation the system will assume.

A number of different modes of operation can be identified for thehybrid drive system according to the invention:

1) The rpm of outer rotor 25, designated n₂ in FIG. 4, is greater thanthe rpm of the inner rotor 24, designated no. The internal combustionengine 21 and the battery 22 cooperate in this case to drive thevehicle. The wheels of the vehicle rotate at an rpm designated n₃. Thishybrid mode of operation is useful, e.g. for rapid acceleration of thevehicle or when driving uphill, since the vehicle wheel torque must thenbe increased, meaning that the CVT must be shifted down. As the CVT hasshifted down, n₂ increases, which means that there must be a speedchange in the energy converter 23 in order to keep the rpm of theinternal combustion engine constant.

2) The rpm n₂ of the outer rotor 25 is equal to the rpm n₁ of the innerrotor 24. This operational mode is of interest in highway driving whenthe vehicle can be driven solely by the internal combustion engine 21.The battery 22 only supplies a direct current to the winding of theouter rotor to maintain the torque which is required. The battery poweris only used to compensate for losses in the energy converter 23.

3) The rpm n₂ of the outer rotor 25 is less than the rpm n₁ of the innerrotor 24. This operational mode is used primarily to charge the battery22.

4) The internal combustion engine 21 is not in operation and the innerrotor 24 is stationary while the outer rotor 25 rotates. In thisoperational mode, the vehicle is driven solely by the energy converter23 and is thus of interest for operation in cities where there arestrict low emission requirements.

5) If a fault should occur in the current-converter 30 or the battery22, the vehicle can be driven by the internal combustion engine 21alone. This is made possible by short-circuiting the three-phase windingin the outer rotor by means of a short-circuiting means 32 of variableresistance which can be coupled in series with the three-phase windingto increase the extractable torque. In this operational mode, the outerrotor 25 lags in relation to the inner rotor 24. The amount of lag isdependent on the torque extracted by the wheel axle 28.

6) Furthermore, the internal combustion engine 21 can be started by thebattery 22 by first locking the outer rotor 25 to the wheel axle 28through the CVT and then using the energy converter 23 as a synchronousmotor for starting the internal combustion engine 21.

7) Starting the internal combustion engine 21 during electricaloperation of the vehicle is done by disengaging the clutch 27 so thatthe inner rotor 24 can begin rotating and by controlling thecurrent-converter 30 so that the desired starting torque and rpm aretransmitted to the internal combustion engine 21. In order to obtain thedesired starting torque, energy is supplied to the energy converter 23from the kinetic energy of the vehicle and from the battery 22.

8) The hybrid drive system can be used as a reserve power source bylocking the outer rotor 25 mechanically or by locking the driving axle28 of the vehicle by means of the vehicle brake system. When theinternal combustion engine 21 drives the inner rotor, the energyconverter 23 works as a generator. Via the slip rings 31 of the outerrotor, the battery 22 can be charged or current can be extractedexternally.

9) Furthermore, a mechanical coupling together of the rotors 24, 25 ispossible. This means that n₂ =n₁. The vehicle is then propelled only bythe internal combustion engine 21. This type of operation is of interestfor highway driving to minimize losses in the system since no currentfrom the battery 22 is required to maintain a constant rpm through theenergy converter 23.

In order to optimize operational properties and to reduce emissions fromthe hybrid drive system, a control arrangement is suggested. FIG. 6shows one embodiment of a control arrangement for a hybrid drive systemaccording to the invention. A control unit 40 for controlling torque andrpm of the internal combustion engine 21 and the energy converter 23emits and receives signals to and from the internal combustion engine 21and the current-converter 30 respectively, and emits signals to atransmission control unit 41 which in turn sends signals to a CVT whichis connected to one of the rotors 24, 25 of the energy converter. Anrpm-estimating unit 42 provides signals for rpm and angular position tothe control unit 40 for regulating torque and rpm. The rpm-estimatingunit 42 can be made with rpm and angle sensors (not shown) at the rotors24, 25 of the energy converter to sense the rpm and angular position ofthe first 24 and second 25 rotors. Alternatively, the rpm-estimatingunit 42 can calculate the rpm and angular position from measuredcurrents and voltages. A pedal position sensor 43, which detects theposition of an accelerator pedal 44 or a brake pedal 45, sends signalsto the control unit 40 for controlling torque and rpm.

A driving strategy unit 46 receives signals concerning suitable drivingstrategy to be selected by an operator, for example the driver of thevehicle, by means of a control panel 47. The driving strategy unit 46sends signals to the control unit 40 for regulating torque and rpm andto the clutch 27. The driving strategy unit 46 receives signals from amonitor 48 which monitors the voltage level and the state of a source ofdirect current, such as a battery 22, and receives signals from a sensor49 which senses the state of the internal combustion engine 21 asregards emissions, fuel/airmixture, engine temperature etc. A display 50can be coupled to the monitor 48 to provide the operator withinformation concerning the condition of the battery 22.

Among the various driving strategies which can be selected from thecontrol panel are hybrid operation, pure internal combustion engineoperation and pure electric operation. The driving strategy unit 46receives the instructions fed via the control panel 47 and providessignals to the various components of the hybrid drive system so that anoptimized operational state is obtained as regards to efficiency andemissions. According to one variation of the invention, the controlpanel 47 permits selection of one of the nine operating modes describedabove.

Various methods of accelerating and retarding the hybrid drive systemaccording to the present invention will now be explained with referenceto FIGS. 4 and 6. When the vehicle is accelerated with the hybrid drivesystem set for hybrid operation, the rotor 25 coupled to the CVT isaccelerated by the kinetic energy of the vehicle when the gear ratio inthe CVT is instantaneously increased via the transmission control unit41. If n₂ is greater than n₁, the current-converter 30 is controlled bythe control unit 40 for regulating torque and rpm so that the rotor 24,which is coupled to the internal combustion engine 21, does not affectthe torque and rpm of the internal combustion engine 21 when the rotor25 coupled to the CVT is accelerated. The battery 22 in this case sendspower to the energy converter 23 when the rotor 25 coupled to the CVTaccelerates. If n₂ is less than n₁, the current-converter 30 iscontrolled so that the charging of the battery 22 is reduced when n₂increases. This results in the torque and the rpm of the wheel axle 28increasing and leaving the torque and rpm of the internal combustionengine constant. The gear ratio can be increased in small increments orin one large increment so that the desired rpm and/or torque is obtainedat the wheels. The torque over the energy converter 23 is constant.

It is furthermore possible to control the torque of the internalcombustion engine 21 within an interval, i.e. that the torque of theinternal combustion engine 21 is increased somewhat so that the outerrotor 25 is accelerated. If n₂ is greater than n₁, the current-converter30 is controlled by the control unit 40 for regulating torque and rpm sothat the battery 22 provides current to the energy converter 23 when theouter rotor 25 coupled to the CVT accelerates. If n₂ is less than n₁,the battery 22 receives power from the energy converter 23. This meansthat the battery 22 will be charged. By controlling thecurrent-converter 30 by means of the control means, this charging can bereduced when the rpm n₂ increases. The gear ratio in the CVT is thenincreased at the same time as the torque of the internal combustionengine 21 is reduced to its original value. This procedure is repeateduntil the desired rpm/torque is obtained and so that the efficiency andemissions from the drive system will be optimum.

An additional possibility for achieving acceleration of the hybridsystem is obtained by accelerating, with the CVT in its disengagedposition, the outer rotor 25 which is coupled to the CVT with the entirepower of the internal combustion engine, or alternatively with afree-wheel clutch arranged between the energy converter 23 and thetransmission 29. When the outer rotor 25 is accelerated to the desiredrpm, the CVT is engaged to accelerate the vehicle. If n₂ is greater thann₁, the current-converter 30 is controlled by the control unit 40 fortorque and rpm control so that the battery 22 provides current to theenergy converter 23 when the rotor 25 coupled to the CVT accelerates. Ifn₂ is less than n₁, the current-converter 30 is controlled so that thecharging of the battery 22 is reduced when n₂ increases. If the rotor 25which is coupled to the CVT should have a higher rpm than is desirablefrom an electrical point of view, its kinetic energy can be used toaccelerate the vehicle by reducing the gear ratio and at the same timecontrolling the current-converter 30 so that the torque is kept constantand so that the internal combustion engine 21 is not braked.

For regenerative braking and when the hybrid drive system is set forelectric operation, the vehicle can be braked by controlling thecurrent-converter 30 so that power is sent to the battery 22 or bydownshifting in the CVT so that the rpm n₂ of the rotor 25 coupled tothe CVT increases due to the kinetic energy of the vehicle. By virtue ofthe fact that the rotor 25 functions as a flywheel, the vehicle's speedthus decreases. The kinetic energy of the rotor 25 can later beredirected to the wheels to accelerate the vehicle.

If the hybrid drive system is set for hybrid drive, the vehicle can bebraked by reducing the gear ratio in the CVT and at the same timecontrolling the current-converter 30 so that when the rotor 25 retards,the torque and rpm of the internal combustion engine 21 will not beaffected. If n₂ is greater than n₁, the current-converter 30 iscontrolled so that the battery 22 gives off energy to the converter 23when the rotor 25 coupled to the CVT is retarded. If n₂ is less than n₁,the current-converter 30 is controlled so that the charging of thebattery 22 increases when n₂ decreases.

FIG. 7 shows one example of an energy converter 23 according to thepresent invention. The outer rotor 25 resembles essentially a stator ina conventional motor but is made to be able to rotate. The outer rotor25 is provided with one or more windings 33 which are fed with currentvia slip rings 31. The inner rotor 24 is made with permanent magnets. Itcan be made so that field weakening can be achieved, which providesincreased maximum speed in pure electric operation. The energy converter23 can also be provided with cooling means to divert the heat generatedin the outer rotor 25.

It should be pointed out that the hybrid drive system can be astationary power source or a power source in a wheeled vehicle or a boatfor example, and that the internal combustion engine in the hybrid drivesystem can be a piston engine or a gas turbine.

What is claimed is:
 1. Hybrid drive system comprising: an internal combustion engine with an output shaft, to which output shaft there is connected, via a coupling, an energy converter having first and second rotors, the rotors being rotatable at different speeds in relation to each other, at least one of said rotors being provided with one or more windings, which are supplied with current via a current-converter, the current-converter being supplied with direct current from a direct current source, and a transmission with variable gear ratio coupled to one of the rotors of the energy converter, wherein the transmission and the current-converter cooperate by means of a control arrangement comprising a control unit for controlling rotational speed and torque of the internal combustion engine and for controlling the energy converter.
 2. Hybrid drive system according to claim 1, wherein in that the first rotor is provided with permanent magnets and the second rotor is provided with the windings.
 3. Hybrid drive system according to claim 1, wherein in that the first rotor is arranged concentrically inside the second rotor and the first rotor is coupled to the output shaft of the internal combustion engine via the coupling and that the second rotor is coupled to the transmission.
 4. Hybrid drive system according to claim 1, wherein in that the coupling is a clutch which can be locked and be prevented from rotating.
 5. Hybrid drive system according to claim 1, wherein in that the winding is a three-phase winding which is supplied with three-phase current.
 6. Hybrid drive system according to claim 5, wherein in that the three-phase winding is provided with engageable short-circuiting means for short-circuiting the three-phase winding.
 7. Hybrid drive system according to claim 1, wherein in that the transmission is coupled to an axle of a vehicle.
 8. Hybrid drive system according to claim 1, wherein in that the transmission is a continuously variable transmission (CVT).
 9. A wheeled vehicle comprising an internal combustion engine with an output shaft, an energy converted coupled to the output shaft via a coupling, the energy converted having first and second rotors, the rotors being rotatable at different speeds in relation to each other, at least one of the rotors being provided with one or more windings which are supplied with current via a current-converter, the current-converter being supplied with direct current from a direct current source, and a transmission with variable gear ratio coupled to one of the rotors of the energy converter, the transmission and the current-converter cooperating by means of a control arrangement comprising a control unit for controlling rotational speed and torque of the internal combustion engine and for controlling the energy converter.
 10. Control arrangement for a hybrid drive system, comprising:a control unit for controlling torque and rotational speed of an internal combustion engine; an energy converter connected to the internal combustion engine via a clutch, the energy converter having first and second rotors which can be rotated at different speeds relative to each other, at least one of the rotors being provided with one or more windings; a current converter supplying current to the rotors, the current converter being supplied with current from a direct current source; a continuously variable transmission coupled to one of the rotors; rotational speed sensors arranged to sense a rotational speed of the first and seconds rotors, the rotational speed sensors sending signals to a rotational speed-estimating unit which provides signals to the control unit for controlling torque and rotational speed; and a pedal position sensor for detecting a position of a pedal and which sends signal to the control unit, the control unit communicating with the internal combustion engine and the current converter and sending signals to a transmission control unit controlling the continuously variable transmission.
 11. Control arrangement according to claim 10, further comprise a driving strategy unit which receives signals concerning a driving strategy, said driving strategy being selected by an operator through a control panel, whereafter the driving strategy unit provides a signal to the control unit for controlling torque and rotational speed and to the clutch, said driving strategy unit receiving signals from a monitor, which monitors the voltage level in the direct current source, and receives signals from a sensor which senses the state of the internal combustion engine.
 12. Control arrangement according to claim 10, wherein the first rotor is provided with permanent magnets and the second rotor is provided with the windings.
 13. Control arrangement according to claim 10, wherein the first rotor is arranged concentrically inside the second rotor, and the first rotor is coupled to the output shaft of the internal combustion engine via the clutch, and the second rotor is coupled to the transmission.
 14. Control arrangement according to claim 10, wherein the clutch can be locked and prevented from rotating.
 15. Control arrangement according to claim 10, wherein the winding is a three-phase winding which is supplied with three-phase current.
 16. Control arrangement according to claim 15, wherein the three-phase winding is provided with an engageable short-circuiting means to short-circuit the three-phase winding.
 17. Control arrangement according to claim 10, wherein the transmission is coupled to an axle of a vehicle.
 18. Control arrangement according to claim 10, wherein the transmission is a continuously variable transmission (CVT). 